As apparatus for forming or shaping food to produce kamaboko (boiled fish paste), sausage, expanded cake, etc., extruders are widely used which thrust and press forward food materials by means of a screw, a pump or the like to extrude the food materials into shapes, from an orifice of a die provided at an extrusion end. In such extruders, the shape of the die orifice may be changed, whereby the food materials can be made into various shapes such as plates, columns, cylinders, etc.
A Japanese food konnyaku or konjak noodles are produced by extruding a konjak paste from a die provided with a number of orifices so as to be formed into noodles, and then immersing the formed or shaped product in hot water to thermally solidify it to a final product.
Thus, the conventional food extruders are all based on the principle that a pressure is applied to food materials in the interior of an apparatus so that the food materials are extruded from the die orifice into shapes.
Since, however, in such conventional food extruders a food material is thrust or pressed out of a die by the action of internally applied pressure, the food material, once thrust out, has a larger diameter than the orifice diameter of the die. For example, in the case where the food material is extruded into linear shapes, they each usually have, though depending on the degree of pressure, a diameter of about twice the orifice diameter of the die. If on the other hand the orifice diameter of the die is made small so that the resulting linear food products can have a small line diameter, clogging tends to occur and also the forming efficiency is lowered. Thus, it has been difficult to form food materials into very thin linear products or into very thin sheets by the use of the extruders.